CODEWITHSUNDEEP
c++multithreadingqtinterlocked
mentalmushroom
mentalmushroom

Reputation: 2467

What operations are called interlocked?

I am trying to make it clear for myself what "interlocked" exactly means. I read the following: "The interlocked functions provide a simple mechanism for synchronizing access to a variable that is shared by multiple threads. They also perform operations on variables in an atomic manner."

So could the following functions be called interlocked?

#include <QtCore>
#include <QAtomicPointer>

QAtomicInt i;

void interlockedMultiply(int factor)
{
    int oldValue;
    do
    {
        oldValue = i;
    } while (!i.testAndSetOrdered(oldValue, oldValue * factor));
}


long long x;
QReadWriteLock lock;

void interlockedAdd(long long y)
{
    lock.lockForWrite();
    x += y;
    lock.unlock();
}

If no, suggest a proper name, please.

Upvotes: 3

Views: 797

Answers (2)

Kuba hasn&#39;t forgotten Monica
Kuba hasn&#39;t forgotten Monica

Reputation: 98485

It's not deceptive to name these functions as such, but you should still document their semantics, preferably using some sort of a formal description that supports concurrency primitives.

Upvotes: 0

Sven Nilsson
Sven Nilsson

Reputation: 1869

Interlocked means that concurrent operations will yield the expected result. I.e. if you perform an interlocked addition five times, the variable will have been incremented five times. Not more, and not less.

Upvotes: 1

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